Image stabilization assembly for an optical system

Abstract

An arrangement for stabilizing the line of sight in an optical tracking system relative to inertial space over a specified range of frequencies utilizing a mirror/torquer/pickoff subassembly both as an inertial sensor and as a control effector.

I claim: 
     
       1. An assembly for rejecting environmental perturbations in an optical system which tracks a command line of sight, comprising: a mirror;   a rigid block;   means for flexibly coupling the mirror to the rigid block, the flexible coupling means providing two axes of rotational freedom for the mirror;   torquer means for torquing the mirror about each of said axes;   pickoff means for sensing the angular position of the mirror relative to the rigid block about each of said axes and providing pickoff signals corresponding thereto; and   control means receiving the pickoff signals and utilizing the dynamic properties of the mirror as coupled to the rigid block and the dynamic properties of the rigid block for providing a torquer signal for each of said axes to said torquer means, the control means utilizing the mirror in conjunction with the torquer means and the pickoff means as an inertial sensor to provide a measure of the angular motion of the rigid block, and as a control effector means to isolate the line of sight from unintentional, higher frequency rigid block motion and to cause the optical system line of sight to track intentional, lower frequency rigid block motion.   
     
     
       2. The assembly according to claim 1 wherein the control means comprises a respective compensator for each of said axes, each compensator utilizing the respective pickoff signal to calculate a plurality of estimated states used for generating the respective torquer signal, the plurality of estimated states including at least mirror angle, mirror angular rate and rigid block angle. 
     
     
       3. The assembly according to claim 2 wherein each compensator multiplies each calculated estimated state by a respective gain coefficient and sums the results to generate the respective torquer signal. 
     
     
       4. The assembly according to claim 3 wherein each compensator subtracts the rigid block angle estimated state from the mirror angle estimated state to derive an estimated pickoff angle signal which is then subtracted from the respective received pickoff signal, the result being utilized for calculating the plurality of estimated states. 
     
     
       5. The assembly according to claim 4 wherein each compensator contains a model of the mirror and flexible coupling means in which the estimated pickoff angle signal is multiplied by the ratio of the angular spring rate of the flexible coupling means to the mirror inertia and the result is subtracted from the result of dividing the torquer signal by the mirror inertia for calculating the mirror angular rate estimated state. 
     
     
       6. The assembly according to claim 2 wherein the plurality of estimated states further includes the integral of the rigid block angle. 
     
     
       7. The assembly according to claim 2 wherein the plurality of estimated states further includes the rigid block angular rate. 
     
     
       8. In an optical system including a mirror, a method for rejecting environmental perturbations to the system and tracking a command line of sight, the method comprising the steps of: flexibly coupling the mirror to a rigid block to provide two axes of rotational freedom for the mirror;   providing torquer means for torquing the mirror about each of said axes;   providing pickoff means which generates pickoff signals corresponding to the angular position of the mirror relative to the rigid block about each of said axes; and   controlling the torquer means by receiving the pickoff signals and utilizing the dynamic properties of the mirror as coupled to the rigid block and the dynamic properties of the rigid block to provide a torquer signal for each of said axes to said torquer means, wherein the mirror is utilized in conjunction with the torquer means and the pickoff means as an inertial sensor to provide a measure of the angular motion of the rigid block, and as a control effector means to isolate the line of sight from unintentional, higher frequency rigid block motion and to cause the optical system line of sight to track intentional, lower frequency rigid block motion.   
     
     
       9. The method according to claim 8 wherein the step of controlling includes, for each of said axes, the step of utilizing the respective pickoff signal to calculate a plurality of estimated states used for generating the respective torquer signal, the plurality of calculated estimated states including at least mirror angle, mirror angular rate and rigid block angle. 
     
     
       10. The method according to claim 9 wherein the step of controlling further includes the steps of: multiplying each calculated estimated state by a respective gain coefficient; and   summing the results to generate the respective torquer signal.   
     
     
       11. The method according to claim 10 wherein the step of controlling further includes the steps of: subtracting the rigid block angle estimated state from the mirror angle estimated state to derive an estimated pickoff angle signal;   subtracting the estimated pickoff angle signal from the respective received pickoff signal; and   calculating the plurality of estimated states by utilizing the results of the second subtraction.   
     
     
       12. The method according to claim 11 wherein the step of controlling utilizes a model of the mirror and flexible coupling means for calculating the mirror angular rate estimated state, in which model the estimated pickoff angle signal is multiplied by the ratio of the angular spring rate of the flexible coupling means to the mirror inertia and the result is subtracted from the result of dividing the torquer signal by the mirror inertia. 
     
     
       13. The method according to claim 9 wherein the calculated plurality of estimated states further includes the integral of the rigid block angle. 
     
     
       14. The method according to claim 9 wherein the calculated plurality of estimated states further includes the rigid block angular rate.